Bent components are used in manufacturing many different types of articles and machines. For example, many of the fluid conduits in an automobile are bent to a predetermined shape for installation on an automobile assembly line. In such situations the component must be shaped to exacting tolerances, particularly in the case of for example brake lines which carry brake fluid from the master braking cylinder to the wheel cylinders, in order to ensure that the conduits fit into the space for which they are designed and conduits are stable in motion.
One popular bending method is known as “draw bending”, in which the workpiece is held in position and bent by a bending arm around a dye having a set radius of curvature. Where multiple bends are required in different directions, rather than changing the direction of motion of the bending arm and the orientation of the dye, after each bend the workpiece is rotated to the next bending plane so that the bend can be effected by actuating the bending arm in the same direction, to the desired angle. Such a device is known as a “rotary draw bender.”
To bend components within very high tolerances, rotary bending heads have been developed that combine different types of actuators, for example a hydraulic gripper for gripping the tube can be combined with an electric motor for rotating the tube to the bending plane and pneumatic or hydraulic actuators for effecting the actual bending of the tube by the bending arm.
A conventional rotary bending head comprises a set of jaws for gripping one end of the tube; a bending arm extending forwardly of the jaws and having a grasping end, for holding the tube during bending and rotation; and a dye having a specific bending radius movable to the bending point on the tube, the dye being sized depending upon the diameter of the tube and the desired radius of curvature of the bend. The arc of motion of bending arm is limited to the bending plane, so the tube is rotated until the desired bend direction falls into the bending plane, at which point the bending arm is actuated to effect the bend to the desired angle. In a typical case this process occurs multiple times on a particular tube, for example in the case of a brake line.
However, such prior art rotary bending heads have significant limitations. The time that it takes to apply multiple bends to a tube depends upon a number of factors, including the rotational speed of the bending jaws. Prior to each bend, the jaws must rotate the tube to an angular orientation in which the desired bend direction lies in the bending plane. This rotation cannot commence until the previous bend is completed, and in order to maintain precise tolerances the rotation must completely cease before the next bend begins. In the case of a tube to which multiple bends are to be applied, the time spent rotating the tube to the bending position for each successive bend can constitute the majority of the time taken to complete the bending process. In industries such as the automobile parts industry, where a typical run through the bending apparatus to fill a single order can involve hundreds of thousands of tubes, this wasted time can have a significant unnecessary overhead cost.
Moreover, the tube bending head so described as capable of bending tubes only up to a certain length, i.e. approximately 1.3 meters (4 feet), at the maximum rotational speed of the jaws. Because of the mechanical disadvantage obtained by grasping the tube at one end, in longer tubes the inertia of the free end of the tube will cause the tube to wobble, to the point where the tube is likely to be out of alignment at the moment the bend occurs, unless the rotational speed of the jaws is reduced. With the jaws rotating at maximum speed, as a long tube is rotated the free end of the tube tends to twist and lag behind the gripped end of the tube, so that the bending point may not have rotated fully into the bending plane at the precise moment that the bending arm is applied to the tube. Also, if the tube is heavy enough inertia can cause the tube to slip in the gripper at full speed. All of these problems result in reduced tolerance and, in many cases, inaccurate bends, which requires that many of the component be discarded. This problem is also wasteful and time consuming over many thousands or hundreds of thousands of workpieces.
It would accordingly be advantageous to provide a bending apparatus that is capable of maintaining high rotational speeds when rotating the tube into the bending plane over successive bends, without reducing the accuracy or tolerances in the finished product, and to be capable of bending tubes longer than 1.3 meters (4 feet) quickly and without reducing the accuracy or tolerances in the finished product.
Further, it would be advantageous to provide a series of bending heads in an apparatus, in order to effect bends of many different radii and complete the entire bending procedure without having to change the bending dye. However, positioning each bending stations far enough away from adjacent bending stations so that the workpiece can be bent without interference by an adjacent bending station would take up considerable floor space.